Growths of sessile organisms such as mussels are of frequent occurrence on the walls of water pipes. Their presence is unwelcome mainly for two reasons: first because by reducing the effective bore of the pipe and increasing the roughness factor, they diminish the water carrying capacity of the system, and second, through setting up local differences in the state of oxidation on the inner surface they can be responsible for electro-corrosion of steel and cast-iron pipes. These consequences are responsible for much waste in the water supply industry in increased pumping costs, loss of water carrying and treatment capacity, in pipe cleaning, maintenance and replacement. Similarly, in the electrical power generation, the chemical, refinery and other industries they are responsible for diminished cooling capacity, lower production capacity and the more frequent cleaning maintenance and replacement.
The Zebra Mussel is dark brown or black in color, and often has a very pretty arrangement of brown and fawn stripes, hence its name of Zebra Mussel. It attaches itself to firm objects such as water pipes by up to 200 tough fibers of a dark horny material (the byssus) and usually leads a sessile existence. Frequently the mussels fix these lyssel threads to other mussels, thus forming clusters in open water, and layers of up to a foot or more on walls and pipes.
The earliest published reference to Dreissena polymorpha dates to the mid-eighteenth century when their presence in the northern Caspian Sea and the Ural River was described by Pallas. The mussel has since spread relentlessly throughout central and southern Europe and is making inroads in the southern portions of Scandinavia and eastward into Asia.
Dreissena polymorpha was unknown in the Laurentian Great Lakes prior to 1988 when substantial infestations were discovered in southeastern Lake St. Clair. Presumably, the mussels were introduced with ballast water discharged from the tanks of international shipping about two years earlier. They have spread throughout Lake Erie with phenomenal speed and reports of their presence at Green Bay, Wis. and Gary, Ind. on Lake Michigan imply that it is only a matter of time before all the Great Lakes and the adjacent Mississippi and Ohio River Basins are affected. With time, the threat may extend to every body of surface water in North America.
The explosive development of the mussel population in western Lake Erie has prompted dire predictions for the future. The number of animals per unit area promises to increase exponentially, especially during the years immediately following the initial infestation.
Various methods have been proposed for the removal of existing growth of the Zebra Mussel such as by scraping the mussels from mains and tanks. This method is not only slow and expensive but the greatest drawback is that it cannot be expected to remove every mussel from the pipe mains and cooling or heat exchange equipment. Moreover, it means that the pipe mains and other equipment cannot be in service during the treatment intended to remove the Zebra Mussel.
Chlorine has been proposed for the removal of the mussels and dosing of the water with up to 50 ppm chlorine as it flows through the main for periods upwards of two weeks has been shown to be a reliable method of control.
However, the use of chlorine for such purposes has certain obvious disadvantages since it is quite toxic to humans and animals and is corrosive to the operating equipment. It produces undesirable often toxic, even carcinogenic, chlorinated organic compounds in the water.
It would be highly desirable, therefore, if an improved process could be developed for controlling the infestation of the Zebra Mussel without the use of laborious time-consuming scraping or pigging operations or the use of materials which are toxic to humans and animals and are corrosive to the operating equipment.
It would also be highly desirable if an improved process could be developed that would permit the use of a non-toxic material that would effectively remove the Zebra Mussel from water pipes and other waterworks with a minimum of difficulty, time and expense.
It is, therefore, an object of the present invention to provide an improved process for controlling Zebra Mussel infestations with the use of a material which is non-toxic to humans and animals.
It is a further object of this invention to provide a novel process for removing infestations of the Zebra Mussel in water pipes and waterworks in the water cooled equipment, heat exchangers, condensers and piping of power plants, chemical plants and other industrial equipment that is efficient and relatively inexpensive and does not involve disruption of the water system to the consuming public.
These and other objects of the present invention are readily achieved by the process hereinafter described.